1. Field of the Invention
The present invention relates to a washing machine automatically executing an operation including the steps of washing, rinsing and dehydration in order, optionally followed by the step of drying, and turning power off at the end of the automatic operation.
2. Description of the Background Art
A drum-type washing machine executes an automatic operation including the steps of washing, rinsing, dehydration and drying in this order. The operation will be described with reference to FIG. 11. First, a user turns on a power key, the power is fed to a control circuit (step SA1, hereinafter, “step” will be omitted), and input course and settings of operation, for example, are displayed. At this time, water level in a water tank is detected (SA2). When water level higher than an arbitrarily set level (which will be referred to as door-open prohibiting level) is detected, the door is locked (SA3). When the water level in the water tank is higher than the door-open prohibiting level and the user opens the door carelessly, water leaks out from the water tank to the outside of the washing machine. Therefore, the door is kept closed to prevent water leakage. Then, a drainage pump is activated (SA4) to drain off the water left in the water tank to a reset water level (SA5). After the end of drainage, operation of the drainage pump is stopped (SA6) and the door lock is released (unlocked) (SA7).
After the door lock is released, or when water level higher than the door-open prohibiting level is not detected, the door may be opened, and therefore, the user opens the door, put in the laundry and closes the door. When the user inputs a change in the course or settings of operation at this stage, setting of operation conditions is changed (SA9). When, the start key is operated (SA10), the door is again locked (SA11), water feed starts, and the operation proceeds from the step of washing through rinsing, dehydration to drying.
When the operation ends (SA13), function of all loads including a motor, a pump, a fan, and a water feed valve are turned off (SA14), door lock is released (SA15), power supply to the control circuit is stopped (SA16) and the power is turned off (SA17).
When the water feed valve is out of order or blocked up by foreign matters such as dust or sand, the function of shutting-off water cannot properly be attained even when the power is turned off to close the water valve at the end of operation. Consequently, water leaks from the water feed valve and the water builds up in the water tank. This leads to a trouble that the water overflows from the water tank and flows to the outside of the washing machine, or water flows down when the door is opened while the power of the washing machine is off.
As a solution, Japanese Patent Laying-Open No. 2001-347093 discloses, in paragraphs [0024] and [0025], a technique in which after the end of a series of operations in a washing machine, when it is detected that a prescribed water level is reached in the water tank, the power is turned on, the door is locked and the water is drained off.
As described above, in the conventional washing machine, water level of the water tank is detected, and various measures are taken to prevent water leakage from the water tank. In view of the foregoing, some conventional washing machines have a function of continuously monitoring leakage at a water feed valve in a standby state (while not in operation).
In order to continuously monitor water leakage in the standby state of the washing machine, it is necessary to feed power to a water level sensor continuously, in the standby state of the washing machine.
Though the user wishes to know any water leakage, he/she also wishes to save power consumption of the washing machine as much as possible.